- After photons, they are the most abundant particles in the universe. Among the known fundamental particles, they are also perhaps the strangest.

-They interact very feebly with other particles. Therefore, all forms of matter, including the earth, are nearly transparent to them.

-About 100 trillion neutrinos from the sun and other cosmic sources pass through our bodies every second without causing any harm.

It is now known that neutrinos come in three types (electron-neutrino, muon-neutrino and tau-neutrino). Once thought to be massless, they are now known to have very tiny masses. But their individual masses remain unknown. Of the three neutrino flavours, the heaviest has at least one 10 millionth the electron’s mass.

Which flavour is the heaviest? The ordering of neutrino masses too is unknown. This is called the ‘mass hierarchy’ question, which the INO is well suited to investigate.

What is strange about these particles ?

The strange particles also have the ability to morph from one type to another as they pass through space, people, matter and the Earth itself, rarely interacting with anything in their path. This is called neutrino oscillation. While the details of two oscillations are known fairly well, the third — the switching of tau-neutrino to electron-neutrino — is not well characterised and forms one of the main objectives of the INO.

What is INO (India-based Neutrino Observatory (INO) ?

INO is a multi-institutional collaboration which aims to build an underground laboratory for pure Science research, especially in Neutrino Physics. The project includes construction of an iron calorimeter detector, called ICAL, that will be the world's most massive detector when completed. ICAL at INO holds the key to understanding several fundamental issues regarding the nature and interactions of neutrinos.

The project involves the construction of an underground laboratory, called the India-based Neutrino Observatory (INO), to be located in a cavern under a rocky mountain in the Bodi West Hills region of the Theni district, about 110 km west of Madurai in Tamil Nadu.

The location in Bodi West Hills was chosen as the next best site. The main INO laboratory will be located in a cavern 1.3 km below a mountain peak. There, an entirely indigenously built magnetised iron calorimeter detector, weighing about 50 kilotons, will be used to detect both natural and man-made neutrinos. The cavern will be linked to the outside world by a 1.9 km long main tunnel.+

The idea for a neutrino observatory in India was first mooted in 2000 at an international conference in Chennai. The proposal was further refined and consolidated at the 2001 Neutrino meeting in Chennai, when the INO consortium of collaborating Indian institutions was formed. In 2002, a formal proposal was submitted to the Department of Atomic Energy, which has since been the nodal agency for the project.

The project has now been identified as one of the mega science projects in the XII Plan with an investment of Rs. 1,350 crore by the DAE and the Department of Science and Technology (DST). At present, 26 Indian institutions — which include Calicut University — and about 100 scientists are involved, with the Tata Institute of Fundamental Research, Mumbai, as the nodal institute.

What will INO do ?

In Phase I, INO will study only neutrinos produced by cosmic rays in the Earth’s atmosphere.

In Phase II, it could be used as a far detector for using beams from future accelerator-based ‘neutrino factories’ in Japan, Europe and the U.S. The INO is expected to become operational in 2017 when the first module of the detector will start taking data.